Bay Trees: Laurel Wilt

Recently, the City of Ormond Beach has received inquiries with regard to a tree disease affecting bay trees. The City has consulted with Dr. Don Spence, a plant pathologist and certified municipal arborist, who has been doing research on this disease at the University of Florida. The disease is called “laurel wilt” and it affects all members in the lauraceae plant family, which includes swampbay, scrubbay, redbay, and avocado. Laurel wilt is currently found in most Florida counties with the exception of the western panhandle and southwest Florida. It is also found in North Carolina, South Carolina, Georgia, Mississippi, and Alabama.

Laurel wilt is spread by a very small beetle, approximately 1/16" long, called the redbay ambrosia beetle. The redbay ambrosia beetle finds trees by the unique smell the lauraceae plant family of trees produce. The beetle carries a fungus with it which it feeds on once it bores into a tree. A redbay tree can die within a week after being attacked. Nothing can stop the spread of the beetle because they are so small; to this end, the City does not recommend that insecticides be used to control the beetle.

Fungicide injections have worked for some trees; however, it does not provide a 100% guarantee in saving trees and the fungicide must be injected into the tree before it is attacked by the beetle and infected with the fungus. If the tree is showing signs of wilt, the fungicide will not kill the fungus, and the tree will die if infected by the fungus first. In experimental trials, the fungicide treatment has lasted up to three years; but, for the first few years of exposure, injections should be repeated every year for at least two years. The cost of the fungicide treatment is based on the size of the tree which could make this an expensive option.

In removing trees that have died from the disease, the only restriction is that untreated wood products (dead trees/logs/firewood) cannot be moved more than 50 miles. (Florida Administrative Code, Chapter Title: Firewood and Unprocessed Wood Products; 5B-65) The disease has not been shown to have the ability to contaminate chainsaws or other pruning equipment. Currently, there are no existing state of Florida restrictions that limit who can remove trees infested with the redbay ambrosia beetle and fungus.

There is always the chance a tree may go undetected by the beetle so it is important, if at all possible, to reduce the number of standing dead trees. The best way to reduce the number of beetles is to chip dead trees as soon as they are detected with a standard tree chipper. An experiment found that less than 1% of beetles in a tree will survive being chipped and that the fungus is also killed. The wood chips produced should be covered with a tarp for a week and then could be used for landscaping or as mulch for nature paths with no risk of contaminating healthy trees.

It seems reasonable that burning the dead trees would work, but no experiments have been conducted to test its effectiveness and it is possible that the beetles could detect heat and fly away before being incinerated. As long as dead trees are not moved more than 50 miles, infested wood is fine for use in a fire place. If the wood is going to be stacked for drying, it should be covered with a tarp to trap any beetles in the wood and prohibit other beetles from using it for breeding. Covering the dead trees/logs is extremely important in removing the wood from access by the beetles.

Dead redbay trees can become a hazard to people and property after a few months of dying because redbay wood breaks down more quickly than hardwoods such as oak or hickory. The reason we are advocating immediate removal of dead trees is because a standing dead redbay tree will be a hazard to people and because the beetle and fungus will use it for its breeding grounds for at least a year.
For more information, we encourage you to visit the University of Florida’s EDIS information system (www.edis.ifas.ufl.edu) and search for “laurel wilt.”